1. Field of the Invention
The present invention relates to a semiconductor package, and more particularly to a power module package.
2. Description of the Related Art
A conventional semiconductor package is used after being mounted with one or more semiconductor chips on a chip pad in a lead frame, sealed hermetically with an epoxy molding compound (EMC) to protect the parts therein, and installed on a printed circuit board.
As the speed, storage capacity and integration density of electric machines increases, power devices are required to be smaller and lighter. Moreover, a power device must make less noise and ensure high reliability, so that an intelligent power module package having a plurality of chips used in a power device and a control device in one semiconductor package becomes more common.
FIG. 1 is a sectional view illustrating an intelligent power module package formed by a conventional method. The power module package illustrated in FIG. 1, is disclosed in U.S. patent application No. 5,703,399, entitled xe2x80x9cSemiconductor Power Modulexe2x80x9d, filed on Dec. 30, 1997 by Mitsubishi Corp. Referring to FIG. 1, the power module package has a molded shape, in which a chip 51 for a power device and a chip 53 used in a control device are mounted on a flat leadframe 58, and are bonded to the leadframe 58 with wires 54. In FIG. 1, reference numerals 52 and 57 indicate a metal mold and an EMC respectively, which are used in a first molding process, and 55 and 56 indicate a heat sink and another EMC, respectively. The other EMC 56 is formed in a second molding process and serves as an insulating layer between the heat sink 55 and the leadframe 58. Reference numeral 59 indicates a metal molding used in the second molding process to form the above insulating layer 56.
However, power module packages formed by a conventional method have many problems. Firstly, in the case of a power module package mounted with many chips, to mount a plurality of chips on a flat leadframe, the size of the leadframe and the power module package must increase. But, a large-sized power module package can increase manufacturing costs for assembly. Moreover, a large-sized power module package can cause chip cracking and package warping. Also, it decreases yield, and brings about problems associated with reliability, such as performance deterioration.
Secondly, in forming the insulating layer 56 insulating the leadframe 58 from the heat sink 55 during the second molding process, the thickness of the insulating layer 56 must be as thin as possible to improve the heat property of the power module package. However, if the insulating layer 56 is made to be too thin, the flow of an EMC deteriorates during the second molding process, so that the EMC cannot fill up the space between the leadframe 58 and the heat sink 55 and an air gap (not shown) may easily be formed. The air gap is a major factor which deteriorates the heat property of the power module package by blocking a heat conducting passage between the leadframe and the heat sink. On the other hand, if the insulating layer 56 is made to be thick, it partially blocks heat in the heat conducting passage which connects the chip 51 used in a power device to the leadframe 58 and the heat sink 55, thereby deteriorating the heat property of the power module package.
Thirdly, in case of a power module package formed by a conventional method, two separate molding processes are performed to prevent the package from warping. However, the two molding processes increase the time taken to manufacture the power module package, thereby increasing the cost of production in an assembling process.
Fourthly, a power module package is divided into two parts including a power unit having the chip 51 used in a power device, and a control unit having the chip 53 used in a control device. After the power module package is molded, it is impossible to test the electrical property of the power module package at any time up until the package is processed by a trimming/forming process. Therefore, there is a problem in which if one of the two parts become deteriorated after the trimming/forming process is finished, the power module would be totally defective. Moreover, during processes which precedes the trimming/forming process, it is impossible to perform an interim test without breaking the power module package, so that the yield may be decreased.
It is therefore an object of the present invention to provide an intelligent power module package which can improve the heat property, yield, and reliability and reduce the manufacturing costs by forming the intelligent power module package according to a method in which a power unit and a control unit are separately manufactured and are subsequently stacked.
To achieve the above object of the invention, an intelligent power module package according to an aspect of the present invention, includes a power unit including a heat sink and a control unit is manufactured separately from the power unit and is subsequently stacked on the power unit. Here, the power unit and the control unit which are not processed by a soldering process yet, can be manufactured separately until a wire bonding process is completed or until a trimming/forming process and an electric property test are completed.
Preferably, in the case of an intelligent package having a power unit and a control unit which are separately manufactured until a wire bonding process is completed, the leadframe used in the wire-bonded control unit, is molded so that it is stacked on the leadframe used in the wire-bonded power unit, to form a semiconductor package. Here, the leadframes of the power unit and the control unit are electrically connected with each other in a soldering process performed after the molding process.
It is preferable that in the case of an intelligent package having a power unit and a control unit which are separately manufactured until an electric property test is completed, locking means formed in each of the semiconductor packages of the power unit and the control unit connects the two semiconductor packages, thereby forming one semiconductor package. The leadframes of the power unit and the control unit are also connected with each other in the soldering process.
According to a preferred embodiment of the present invention, instead of being bonded too early, the above heat sink is bonded to the leadframe by inserting an insulating layer under the lower part of the leadframe during a molding process.
According to the present invention, it is possible to improve the heat property, the yield, and the reliability of an intelligent power module package, and to reduce the manufacturing costs, by forming the intelligent power module package in a method in which a power unit and a control unit are separately manufactured and are subsequently stacked.